This invention relates to a playback method in a video disk player and more particularly to a playback method for use in a constant angular velocity video disk player having a disk in which data are recorded in high density.
In a conventional video disk player (hereinafter referred to simply as "VDP"), there have been widely used two modes, constant linear velocity (hereinafter referred to simply as "CLV") and constant angular velocity (hereinafter referred to simply a "CAV") in writing/reading original data on/from a disk. Generally, when the disk revolves at a constant driving speed in the VDP, its linear velocity in the inner boundary of tracks of the disk differs from that in the outer boundary of the tracks. For instance, a sufficient and adequate linear density for recording and playback of data is maintained in the inner boundary of the tracks, while excessively thin density for recording and playback is brought about in the outer boundary of the tracks. Therefore in the CLV mode, the farther the outer tracks are from the center of the disk, the lower its revolution velocity correspondingly goes, so that it is invariably maintained at a constant linear velocity. This CLV mode generally has an extended operating time of playback which gives about one hour per each surface of the disk, but it has a disadvantage of not being capable of providing a variety of functions which are usually requested by users.
On the other hand, the CAV mode makes it possible to provide a variety of functions such as "Still Motion", "Reverse Motion", "Free Variable Control of Speed" and so on, but its playback period of operation is disadvantageously short comparing to that in the CLV mode. Referring to the FIG. 1 illustration of a disk format in the CAV mode in prior art, it includes two synchronization fields 11 and 12, and two data field 13 and 14 respectively. Each surface of the disk is divided into two parts, so only two fields of data that consist of a frame of video signals are read out of each track on the disk, and consequently only about half an hour of operating period of playback is permitted for each surface of the disk.